Most measuring instruments in use today utilize an analog meter in displaying the measured information. While these devices are quite economical, non-linearity in the analog meter movement can produce errors. Additionally, these types of meters are hard to accurately read due to the small size of the meter screen.
Furthermore, most of these analog metering devices contain range switches which must be interpreted along with the reading on the screen. In other words, if the range switch is positioned, for example, on an X10 scale, a reading on the meter must be multiplied by a factor of 10. This calculation is mentally or manually accomplished by the operator and can lead to misreading of the meter, expecially when many readings are taken.
One such metering device is the Victoreen Model 555 radiation measurement system which is currently in use by Food and Drug Administration personnel in determining the exposure achieved by medical X-ray equipment. Although the 555 can be used to make highly accurate measurements, performance is degraded slightly by nonlinearities in the analog meter movement, and errors in determining the scale factor can occur in the midst of multiple tedious test procedures.